The present invention relates to a valve timing control apparatus for an internal combustion engine, and particularly relates to a valve Liming control apparatus that serves to control opening and closing timings of an exhaust valve.
Japanese Patent Application Unexamined Publication No. 2006-207398 A discloses a valve timing control apparatus for an internal combustion engine which includes a drive rotation member (sprocket) synchronously rotatable with a crankshaft, a follower rotation member disposed to be rotatable relative to the sprocket and make a unitary rotation with a camshaft, an electric motor connected to the follower rotation member through a given speed reducer. The valve timing control apparatus is adapted to change a rotational phase of the camshaft relative to the crankshaft by controlling operation of the electric motor in accordance with an operating condition of the engine.
An intake valve and an exhaust valve are provided with valve timings appropriate to engine start which are different from each other. Especially, the exhaust valve must be positioned on a phase-advance side at the time of engine start. Therefore, the valve timing control apparatus of the above conventional art includes a valve timing adjusting mechanism for an exhaust valve in which a biasing member is disposed between the drive rotation member and the follower rotation member. With the provision of the biasing member, the valve timing adjusting mechanism has a failsafe function to change a phase of the exhaust valve to the phase-advance side even when a malfunction of an electric system occurs.